Electrical resistance monitoring device

Abstract

A device for indicating whether a conductive element has an electrical resistance equal to or less than a predetermined value or whether the conductive element is reliably connected to earth reference potential by a resistance equal to or less than a predetermined value. The device includes a clamp device for connecting the device to the conductive element and which incorporates a battery powered monitoring unit. The monitoring unit includes a current-to-voltage converter with a voltage output that is inversely proportional to the resistance of the conductive element, a comparator which compares at predetermined intervals voltage output to a pre-set reference and determines whether the measured resistance is equal or less than the predetermined value, and a signaling device which is actuated to provide an indication as to whether the measured resistance is equal to or less than the predetermined value.

1. A device for indicating whether a conductive element has an electrical resistance equal to or less than a predetermined value or whether the conductive element is reliably connected to earth reference potential by a resistance equal to or less than a predetermined value, said device comprising
 a clamp device for connecting said device to the conductive element;  
 wherein said clamp device incorporates a battery powered monitoring unit comprising  
 a current-to-voltage converter with a voltage output that is inversely proportional to the resistance of the conductive element;  
 a comparator which compares at predetermined intervals said voltage output to a pre-set reference, and determines whether the measured resistance is equal or less than the predetermined value; and  
 a signaling device which is actuated to provide an indication as to whether the measured resistance is equal to or less than the predetermined value, the predetermined value of the measured resistance being in the range 1-100 Ohms.  
 
   
   
     2. A device as claimed in  claim 1 , wherein the clamp device comprises a pair of spring-loaded jaws which are engaged with an available part of the conductive element and contain contacts which are connected to the monitoring unit. 
   
   
     3. A device as claimed in  claim 1 , wherein the predetermined value of the measured resistance is less than 50 Ohms. 
   
   
     4. A device as claimed in  claim 1 , wherein the signaling device is a visual signaling device. 
   
   
     5. A device as claimed in  claim 4 , wherein the signaling device is a lamp which is illuminated continuously or intermittently so long as the measured resistance has a value less than the predetermined value. 
   
   
     6. A device as claimed in  claim 5 , wherein the lamp is a light-emitting diode. 
   
   
     7. A device as claimed in  claim 1 , wherein the battery is a lithium manganese battery. 
   
   
     8. A device as claimed in  claim 1 , wherein the clamp device comprises a pair of spring-loaded jaws which are provided with three point contacts, one of said contacts being provided on one of the clamp jaws and the other two contacts on the other jaw. 
   
   
     9. A device as claimed in  claim 8 , wherein, when the clamp is closed, the two contacts on one jaw lie to either side of the single contact on the other jaw, the three contacts lying substantially in the common plane. 
   
   
     10. A device as claimed in  claim 8 , wherein the two contacts on one of the jaws make electrical contact with the equipment to which the clamp is applied and are connected to the monitoring unit, a third point contact on the other jaw being of insulating material. 
   
   
     11. A device as claimed in  claim 1 , wherein the clamp device is connected to earth by a cable. 
   
   
     12. A device as claimed in  claim 11 , wherein the cable is a two-core cable and the device is adapted to monitor both the connection of the device to the conductive element to which it is applied and also the connection of the device to earth. 
   
   
     13. A device as claimed in  claim 11 , wherein the cable is a single-core cable and the device is adapted to monitor only the connection of the device to the conductive element to which it is applied.